Manually controlled case depth measuring instrument with indicators to guide its use

ABSTRACT

A case depth measuring instrument for measuring the depth of the hardened layer of a steel to be tested, by impressing a D.C. magnetic field on said steel locally from its external quenched surface, measuring the magnetic flux of said field by means of a hall element while varying the magnetomotive force of said field and reading the value of the coercive force of said field at the point when the magnetic flux has reached zero.

United States Patent Kurose et al.

[451 Sept. 5, 1972 [54] MANUALLY CONTROLLED CASE DEPTH MEASURINGINSTRUMENT WITH INDICATORS TO GUIDE ITS USE [72] Inventors: TadashiKurose; Ryuichi Kagaya, both of Katsuta; Kunio Ono; Kimio Kanda, both ofHitachi, all of Japan [73] Assignee: Hitachi, Ltd.,Marunouchi,Chiyodaku,Tokyo, Japan 221 Filed: March 17,1970

21] Appl.No.: 20,218

[52] US. Cl. ..324/34 R [51] Int. Cl. ..G0lr 33/12 [58] Field of Search..324/34 R, 34, 45, 40

[56] References Cited UNITED STATES PATENTS 3,490,033 l/ 1970 Elarde..324/34 R 2,097,947 11/ 1937 Fahy ..324/34 R FOREIGN PATENTS ORAPPLICATIONS 871,185 311953 Germany ..324/43 OTHER PUBLICATIONSMcMaster, R., Nondestructive Testing Handbook; Vol. II The Ronald Press;1963, New York, pp. 34.1, 34.2, 34.3. A

McMaster, R., Nondestructive Testing Handbook, Vol. 11, The RonaldPress, 1963, New York, pp. 34. 1, 34.2, 34.3, 34.5.

Primary ExaminerRobert J. Corcoran Attorney-Craig, Antonelli and Hill[57] ABSTRACT A case depth measuring instrument for measuring the depthof the hardened layer of a steel to be tested, by impressing a DC.magnetic field on said steel locally from its external quenched surface,measuring the magnetic flux of said field by means of a hall elementwhile varying the magnetomotive force of said field and reading thevalue of the coercive force of said field at the point when the magneticflux has reached zero.

3 Claims, 6 Drawing Figures PATENTEDSEP 5 I972 sum 2 as 5 G0 CHECKINVENTOR TADASHI kukosa RYMICHI KAGAYA) Ku/vra o/vo zn l r ro KANAA 4 7,W MQ/ w ATTORNEY MANUALLY CONTROLLED CASE DEPTH MEASURING INSTRUMENTWITH INDICATORS TO GUIDE ITS USE BACKGROUND OF THE INVENTION The presentinvention provides means for nondestructively determining the depth ofthe hardened layer or carbon content, of a given steel.

As this type of means, there has generally been employed a method whichcomprises preparing a small test sample by destroying a piece of thesteel to be tested and conducting a hardness test by mechanical means orchemical analysis on said sample piece to determine the property of thesteel. The method,-therefore, has the big drawback that not only was theoperation efficiency very low, but also the method was not applicable tocertain types of-steel.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is agraph showing the hysteresis curves of steel;

FIG. 2 is a graph showing the relationship between the hardness and thecoercive force, and the depth of hardened layer, of steel, for thepurpose of explaining the principle behind the present invention;

FIG. 3 is a diagram showing the construction of one embodiment of thepresent invention;

FIG. 4 is a diagram showing the construction of another embodiment ofthe invention;

FIG. 5 is a graph showing the hysteresis curves of steel, for explainingthe embodiment of FIG. 4; and

FIG. 6 is a graph exemplifying the result of the actual measurement on aquench hardened layer, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 which showsthe magnetic hysteresis curves of steel at a hardened portion and anunhardened portion respectively, symbol Hc indicates the coercive forceof the unhardened portion and He the coercive force of the hardenedportion. In general, the coercive force is greater at the hardenedportion than at the unhardened portion.

Further, as will be seen from the experimental results of FIG. 2, thecoercive force of steel decreases with the hardness which varies as thedepth from the quenched surface increases. In FIG. 2, symbol Bmax is themaximum flux B in FIG. 1.

Generally speaking, a hardened layer is not distinctive in forged steelrolls, etc., as shown in FIG. 2. Namely, the steel shows a substantiallyconstant high hardness to a certain depth from the surface thereof andthen the hardness decreases gradually as the distance from the surfaceincreases. However, since the coercive force varies with hardness, theapproximate depth of the hardened layer can be judged by penetrating amagnetic flux sufficiently deeply from the steel surface and thenmeasuring the'mean coercive force of the flux penetrating portion.

An embodiment of the present invention, which measures hardnesspenetration based upon the abovedescribed principle, will be describedhereunder:

With reference to FIG. 3, reference numeral 1 designates a steel having,for instance, a hardened layer 2. Reference numeral 3 designates a Hallgenerator for detecting a magnetic flux, which is mounted in a leg of amagnetic field producing electromagnet 4. Reference numeral 5 designatesan exciting coil for the electromagnet 4, and 6 designates a DC. powersource which supplies positive and negative D.C. currents to saidexciting coil. Reference numeral 7 designates a variable resistor havinga contact 9, through which the variable DC. current is supplied to theexciting coil 5. Reference numeral 8 designates an ammeter to measurethe exciting current, 10 a voltmeter to measure the output voltage ofthe Hall generator 3, and 11 an on-off switch for the power source 6. k

With the construction described above, a current Im is, first of all,supplied to the coil 5 from the power source 6 through the resistor 7and the ammeter 8, upon turning the switch 11 on, thereby to excite thehardened layer 2 sufficiently to a point A shown in FIG. 1. Then, theoutput voltage of the Hall generator 3 is reduced to zero, by moving thecontact 9 of the resistor 7 in an opposite direction while watching thevarying output of said Hall generator on the voltmeter 10, whereby themagnetic position of the hardened layer reaches to a point B of FIG. 1.Namely, with Ic representing the current at this time and N representingthe number of turns of the coil 5, the product of 10 X N has a closerelation with the product of H0 X d, wherein He stands for the coerciveforce of the hardened layer and d stands for the depth of said hardenedlayer. The depth of the hardened layer of the steel can be measuredbased on this relation.

According to this type of instrument, the measurement accuracy can beenhanced by increasing the sensitivity of the Hall generator 3.

In measuring the coercive force of the magnetic circuit in the mannerdescribed, if a material having a very small coercive force, such aspure iron, is used for the core of the electromagnet 4, the coerciveforce measured will directly represent the coercive force of the steel 1to be measured. Further, by selecting the electromagnet 4 in such amanner as to penetrate the magnetic flux sufficiently deeper than thedepth of the hardened layer from the surface of the steel 1, themeasured coercive force is shown in its mean value, and the hardenedportion and the portion deeper than that show different coercive forcesas shown in FIG. 2. After all, the measured coercive force correspondsto the depth of the hardened layer. Therefore, if the instrument ispreviously calibrated based on a test piece having a specific hardnesspenetration, it is possible to measure the depth of the hardened layer agiven steel accurately and non-destructively in a highly efficientmanner.

As described above, the present invention makes use of a hall generatorfor the measurement of a magnetic field, so that the magnetic field canbe measured with high sensitivity and hence the depth of the hardenedlayer can be measured with high sensitivity. In addition, since the Hallgenerator is small in size, the space required for the insertion of saidgenerator is very small. This is advantageous in minimizing the errorcaused by flux leakage at the space or the consumption of theelectromotive force by the space. It is, thus, possible to obtain anon-destructive steel testing instrument for measuring the depth of thehardened or penetration layer, which is highly accurate and compact insize.

In the practice of hardening, it is a general requirement that thesurface hardness and hardness penetration of the hardened steel fall inpredetermined ranges respectively. The surface hardness can be measuredby a hardness meter. Therefore, the depth of the hardened layer ismeasured practically on those steels whose surface hardnesses are withinthe predetermined range. According to the experiments conducted by thepresent inventors, it has been confirmed that, with the presentinstrument of the type described above, the depth of the hardened layercan be measured very accurately, with a fluctuation of only i percent.

FIG. 4 shows another embodiment of the present invention which is animprovement over the preceding embodiment of FIG. 3 in that the circuitarrangement is modified to facilitate the practical use of theinstrument. Namely, the embodiment of FIG. 3 is of a construction whichmerely shows the principle of this invention. Therefore, it will havethe following disadvantages, if it is used as such.

I. If the on-off switch 11 is inadvertently turned on, with the contact9 of the resistor 7 being located at either end of said resistor, theelectromagnet 4 is abruptly excited concurrently with the switchoperation. The electromagnet is generally imparted with a magnetizingforce of several thousand ampere-turns for the sake of stablemeasurement, so that its attractive force for magnetic materials isextremely large. Therefore, if the electromagnet is not on the steel tobe measured but, for example, on a desk, there is the danger of themeasurer having his finger injured by being pinched between theelectromagnet and a screw-driver, cutting pliers or other magnetizablematerial attracted by said electromagnet.

2. In exciting the steel to be measured up to the point A in FIG. 5, itis advantageous to maintain the magnetic flux, impressed on the steelfrom the electromagnet, constant for enhancing the accurancy of themeasurement value. To excite the steel unnecessarily vigorously to apoint A or to excite the same to a leaser extent as at a point A" isundesirable. At any rate, the excitation should be effected from thezero position to a predetermined magnetized state.

3. The value of the measurement taken at the point B in FIG. 5, i.e., [0X N, is very small relative to the magnetizing force of several thousandampere-turns of the magnet at the point A of excitation, and is onlyseveral hundred ampere-turns. It is, therefore, preferable to provide apower source to obtain the magnetized state represented by the point Aand a power source to obtain the magnetized state represented by thepoint B separately from each other. However, in order to obtain themagnetized state at the point A, it is always desirable to increase themeasuring current progressively from the zero until finally themagnetized state reaches the point B. This is because, if the point B inadvertently passed and the magnetized state of the steel -has reached,for example, a point E, the magnetized state cannot be returned to thepoint B but is shifted to a point F, even when the measuring current isdecreased, and a large measurement error will result.

Such phenomenon is inevitable by reason of the hysteresis characteristicof magnetic materials. It is, therefore, essential that the measuringcurrent is added slowly from a value above zero, which is at leastsmaller than the value which will have been determined as result.

The above-described precautions are applicable not only to the points Aand B, but also to the points C and D, and are generally hard toexercise for the measurer, even if they are explicitly mentioned in adirection or the like which explains the handling procedure of theproduct instrument. Thus, failure resulting from inproper handling oftenbecomes a problem.

As contrasted, the instrument according to the present invention enablesthe observer to attain the desired measurement in a satisfactory manner,without giving any particular precaution even when such operationalprecautions as set forth above are not fully made known to the observer.The present invention will be described hereinafter with reference tothe embodiment shown in FIG. 4.

Referring to FIG. 4, reference numeral 1 designates a rotary switchcomprising fixed contacts a-h and a'h', and movable contacts 30, 31.This rotary switch 1 provides the following circuit conditions byvarious combinations of the movable contact positions specified below:

Positions a, a The instrument can be connected with the power source inthese positions. Whether the condition should be advanced to the nextstage or not is determined.

Positions b, b The conditions for the first excitation are arranged.Namely, the state of the point A in FIG. 5 is created.

Positions c, c Whether the condition should be advanced to the nextstage or not is determined.

Positions d, d The conditions for the first measurement are arranged.Namely, the point B in FIG. 5 is measured.

Positions 2, e Whether the condition should be advanced to the nextstage or not is determined.

Positions f, f The conditions for the second excitation are arranged.Namely, the state of the point C in FIG. 5 is created.

g, g Whether the condition should be advanced to the next stage or notis determined.

Positions h, h The conditions for the second measurement are arranged.Namely, the point D in FIG. 5 is measured.

The construction and the function of the embodiment of the presentinvention will be described tact 5. Reference numeral 6 designates aslide transformer having a sliding member 7, and 8 designates amicroswitch to detect the zero-position of the sliding member 7, whichis mechanically connected with said sliding member. Reference numerals 9and 10 designate indicator lamps to illuminate CHECK and GO sign platesrespectively, 11 an electromagnet having an exciting coil 12, and 13relay to operate normally opened contacts 14 and 15. Reference numeral16 designates an A.C. power source, 17 a rectifying circuit, 18 a Hallgenerator mounted within the magnetic field of said electromagnet 11, 19a voltmeter to indicate the output voltage of said Hall generator 18,and 20 a variable resistor having sliding member 21. Reference numeral22 designates a microswitch to detect the zero-position of the slidingmember 21 of the variable resistor 20, which is mechanically connectedwith said sliding member 21, and 23 designates a relay to operate anormally opened contact 24. Reference numeral 25 designates a powersource transformer, 26 a rectifying circuit, 27 an ammeter to measurethe current flowing through the exciting coil 12, and 28 a relay toswitch a contact 29. Reference numerals 30 and 31 designate the movablecontacts of the rotary switch 1, as previously stated.

The instrument of the invention constructed as described is operated inthe following manner:

After connecting the instrument with the power source by operating therotary switch 1 to engage the movable contacts 30, 31 with the fixedcontacts a, a respectively and turning the on-off switch 2 on, the pushbutton switch 3 is depressed, whereupon the relay 4 is energized tobring the contact 5 into a closed position.

As a result, the relay 4 is self-held by the contact 5 and will not bereturned to the original position unless the on-off switch 2 is opened.If the sliding member 7 of the slide transformer 6 is not in itszero-position, the microswitch 8 which detects the position of saidsliding member 7 is held in engagement with the pole shown, so that thelamp 9 is turned on to illuminate the CHECK sign plate. On the otherhand, if the sliding member 7 is in its zero-position, the lamp 10 isturned on to illuminate the GO sign plate.

Namely, with the rotary switch 1 being in the positions 0, a theinstrument can be connected with the power source safely, without givingany electric input to the coil 12 of the electromagnet 1 1.

Furthermore, when the sliding member 7 of the slide transformer 6 is notin the zero-position, which slide transformer controls the excitingpower source so that the excitation in the following state may beeffected from the zero-position, the CHECK sign plate is illuminated,urging the observer to bring said sliding member 7 to the zero-position.

If the sliding member 7 is in the zero-position, the GO sign plate isilluminated, assuring that he can advance the rotary switch 1 to thenext stage with a sense of security.

When the rotary switch 1 is shifted to the positions b, b, the relay 13is actuated to close the contacts 14 and 15. Here, the sliding member 7of the slide transformer 6 is rotated, whereupon an A.C. voltagecorresponding to the rotational angle of said sliding member 7 isimpressed from the A.C. power source 16. The A.C. voltage is rectifiedby the rectifying circuit 17 and the resultant DC. current is suppliedto the coil 12 of the electromagnet 11 to excite the same. By theforegoing operation, the steel to be measured is excited tothe point Aof FIG. 5. Whether the steel has been excited to the point A or not isdetected by the Hall generator 18 provided within the magnetic field ofthe electromagnet 11, and is confirmed by the voltmeter 19.

Upon completion of the above-described operation, the sliding member 7is returned to the zero-position, whereby the magnetic characteristic ofthe steel to be measured is shifted to the point A in FIG. 5.

Then, the movable contacts 30, 31 of the rotary switch 1 are advanced tothe fixed contacts 0, 0' respectively. At this time, the lamp 9 or 10 isturned on by the microswitch 22 which detects the sliding member 21 ofthe variable resistor 20 being in its zero-position, and by theillumination of the GO sign plate by the lamp 10 thus turned on, thezero-position of the sliding member 21 is confirmed. The observer canadvance the rotary switch 1 to the next stage, once the GO sign platehas been illuminated.

When the movable contacts 30, 31 of the rotary switch 1 have beenadvanced one pitch to the positions d, d respectively, the relay 23 isactuated to close the contact 24, so that the DC. voltage of theopposite polarity, passing through the power source transformer 25 andthe rectifying circuit 26, is controlled by the variable resistor 20 andsupplied to the coil 12 of the electorrnagnet 1 1.

Thus, the sliding member 21 of the variable resistor 20 is started fromits zero-position reliably and thereby the state of the steel is shiftedfrom the point A toward the point B or to bring the indication of thevoltmeter to zero. The reading from the ammeter 27 at the point when theindication of the voltmeter 19 is zero, is the measured current Ic,.

The first measurement is completed by the foregoing step, then themeasurements for the second time can be attained by repeating the sameprocedure as described above and the measured current [C is obtained. Anaccurate current value Ic free from any error can be obtained by takingthe average of the 10 and I0 i.e. [c (Ir: +Ic )/2.

When the movable contacts of the rotary switch 1 are shifted to thepositions f, h, the relay 28 is actuated to switch the contact 29, sothat the exciting current and the measuring current are supplied to theelectromagnet 11 in a polarity opposite to that of the first time.

The above-described operation ,is summarized in the table below, withreference to FIG. 5, wherein I is the position of the rotary switch 1(the positions of the movable contacts); II is the operation in saidposition of the rotary switch; and III is the point in FIG. 5.

The positive polarity power From point B to Positions f, 1' source isexcited point C via point in an opposite E direction Positions 3, gCheck Point C Second measurement is completed upon From point C toPositions h, h exciting the negapoint D tive polarity power source.

FIG. 6 exemplifies the depth of the hardened layer actually measured ona steel, containing 0.84 percent of carbon and 2.1 percent of chromium,which had been subject to an induction heating and subsequent quenching.The ampers turns of the electromagnet is 100 when the number of turns Nof the coil 12 is 1,000 and the measuring current [C is 0.lA. Therefore,the hardness penetration d of the steel, calculated from FIG. 6, is mm.

From the forgoing description, it will be seen that the three problemspossessed by the instrument of FIG. 3 can be totally solved byconstructing the instrument as shown in FIG. 4.

More specifically, the problem mentioned in (1) above can be solved byarranging such that the power can be supplied to the instrument only ata specific position of the rotary switch 1.

The problems mentioned in (2) and (3) above are avoided by the checksconducted prior to the measurement.

It is added that, while the description herein might give an impressionthat the testing instrument according to the present invention isextremely complicated, the actual construction and operation of theinstrument are very simple and easy, and the measurement can becompleted quickly.

As described above, the testing instrument of the present invention isprovided with the functions of determining the time when the power is tobe supplied thereto and confirming the circuit conditions for the nextstage prior to the current supply. Therefore, there can be obtained theadvantages that the measurement accurary can be enhanced and that theoperational error can be avoided completely.

Although the foregoing description of the preferred embodiments of thepresent invention, reference was made particularly to the use of theinstrument for the measurement of the depth of the hardened layer ofsteel, it is to be understood that the use of the instrument is notrestricted only thereto but the instrument can be used for themeasurement of the carbon content of steel by measuring the coerciveforce the steel.

What is claimed is:

1. A case depth measuring instrument for determining the depth of ahardened layer of a steel to be tested comprising electromagnet meansfor impressing a DC. magnetic field on said steel locally from itsexternal quenched surface including an electromagnet having a mainwinding,

a voltage source for energizing said electromagnet,

first circuit means for selectively connecting said voltage source tosaid main winding of said electromagnet including first adjusting meansfor adjusting the magnetomotive force of said electromagnet, secondcircuit means for selectively connecting said voltage source to saidmain winding of said electromagnet in reverse polarity to the firstcircuit means including second adjusting means for adjusting themagnetomotive force of said electromagnet and force measuring meansconnected in series with said second adjusting means for measuring themagnetomotive force of said D.C. magnetic field,

flux measuring means disposed within the magnetic field generated bysaid electromagnet for measuring the magnetic flux of said magneticfield, switching means for selectively actuating said first circuitmeans or said second circuit means, and indicator means responsive tosaid first and second adjusting means for indicating the zero conditionof said magnetomotive force of said electromagnet, whereby the measuredmagnetomotive force at the time the flux measuring means reads zero is ameasure of the coersive force of the steel from which the case depth canbe determined.

2. A case depth measuring instrument as defined in claim 1 wherein saidindicator means includes a first indicator energized when saidmagnetomotive force is zero and a second indicator energized when saidmagnetomotive force is not zero.

3. A case depth measuring instrument as defined in claim 2 wherein saidswitching means includes a multicontact switch connected to said voltagesource and relay means controlled by said multi-contact switch forsequentially enabling said first and second circuit means, saidindicator means being connected to said multi-contact switch so as to beenergized each time prior to the respective enabling of said first andsecond circuit means.

1. A case depth measuring instrument for determining the depth of ahardened layer of a steel to be tested comprising electromagnet meansfor impressing a D.C. magnetic field on said steel locally from itsexternal quenched surface including an electromagnet having a mainwinding, a voltage source for energizing said electromagnet, firstcircuit means for selectively connecting said voltage source to saidmain winding of said electromagnet including first adjusting means foradjusting the magnetomotive force of said electromagnet, second circuitmeans for selectively connecting said voltage source to said mainwinding of said electromagnet in reverse polarity to the first circuitmeans including second adjusting means for adjusting the magnetomotiveforce of said electromagnet and force measuring means connected inseries with said second adjusting means for measuring the magnetomotiveforce of said D.C. magnetic field, flux measuring means disposed withinthe magnetic field generated by said electromagnet for measuring themagnetic flux of said magnetic field, switching means for selectivelyactuating said first circuit means or said second circuit means, andindicator means responsive to said first and second adjusting means forindicating the zero condition of said magnetomotive force of saidelectromagnet, whereby the measured magnetomotive force at the time theflux measuring means reads zero is a measure of the coersive force ofthe steel from which the case depth can be determined.
 2. A case depthmeasuring instrument as defined in claim 1 wherein said indicator meansincludes a first indicator energized when said magnetomotive force iszero and a second indicator energized when said magnetomotive force isnot zero.
 3. A case depth measuring instrument as defined in claim 2wherein said switching means includes a multi-contact switch connectedto said voltage source and relay means controlled by said multi-contactswitch for sequentially enabling said first and second circuit means,said indicator means being connected to said multi-contact switch so asto be energized each time prior to the respective enabling of said firstand second circuit means.